1. Field of the Invention
The present invention relates to purified brine, particularly brine having reduced organic content, and even more preferably reduced chlorate content. The present invention also relates to processes and apparatus for obtaining brine having reduced organic content, and even more preferably reduced chlorate content, and can relate to mineralization of brine. The present invention also relates to improvement of processes and apparatus wherein brine is used in the processes or apparatus so as to include brine therein having reduced organic content, and can also include reduced chlorate content, in brine used therein or brine obtained therefrom. The present invention is useful in various processes and technologies, such as processes involving water, waste water and brine purification, and particularly useful in chlorine/alkali processes, and processes involving conversion of glycerin to epichlorohydrin. Thus, the present invention also relates to processes and apparatus for purification of brine generated by industrial processes. Purified brine may be used in industrial processes such as a chlor-alkali process for electrolytic conversion of brine to chlorine gas and sodium hydroxide or hypochlorite.
2. Discussion of Background Information
In chemical processes, there is a need to obtain a maximum utility of incoming process streams as well as the ability to recycle process streams, or to use by-products from one process in other processes, particularly in nearby processes. Such uses of process streams are environmentally and economically desirable.
Some chemical processes use a brine stream with high organic content, such as total organic carbon (TOC) and high sodium chloride content. For example, some chemical processes result in a TOC of up to about 20,000 parts per million (ppm) with a sodium chloride content of up to about 23% by weight. If the TOC can be significantly reduced in concentration, there is the possibility for recycling the brine stream as a raw material for other processes, such as chlor/alkali processes or other electrolysis processes. The presence of sodium chloride may pose difficulties in the removal of organic compounds from various brine by-product streams because some removal processes may cause deleterious precipitation of the sodium chloride in separation equipment. Also, the presence of the chloride ion may result in the formation of undesirably corrosive or toxic chlorinated organic compounds during chemical treatment to destroy the organic compounds.
The brine stream may also contain a variety of organic compounds, some of which may be difficult to remove by traditional techniques such as extraction or carbon bed treatment.
For example, in the production of epichlorohydrin from glycerin, a by-product brine stream may have a TOC of up to about 2500 ppm, typically about 1500 ppm and a sodium chloride content of up to about 23% by weight, typically about 20% by weight. For the successful implementation of a glycerin to epichlorohydrin process and related waste reduction and economic optimization, the discharge of brine should be integrated in the site environmental strategy. The level of sodium chloride (NaCl) is too high for direct discharge, after TOC removal, to the environment. The concentration of NaCl is also too high for effective biological wastewater treatment without significant consumption of fresh water and a corresponding increase in the necessary capacity of the wastewater operation. The main TOC component of the by-product brine stream is glycerin, with the other compounds contributing to TOC of the brine including glycidol, 1,2-dichlorohydrin, or 1,3-dichlorohydrin, 1-chloro-2,3-propanediol, 2-chloro-1,3-propanediol, epichlorohydrin, diglycerol, triglycerol, other oligomeric glycerols, chlorohydrins of oligomeric glycerols, acetic acid, formic acid, lactic acid, glycolic acid, and other aliphatic acids. The TOC specifications for the usage of this brine by a nearby or on-site chlor/alkali process may be only 10 ppm or less. However, the major component of the TOC is glycerin which is difficult to remove by traditional techniques such as extraction or carbon bed treatment.
U.S. Pat. No. 5,486,627 to Quaderer, Jr. et al discloses a method for producing epoxides which is continuous, inhibits formation of chlorinated byproducts, and eliminates or substantially reduces waste water discharge. The method includes: (a) forming a low chlorides aqueous hypochlorous acid solution; (b) contacting the low chlorides aqueous hypochlorous acid solution with at least one unsaturated organic compound to form an aqueous organic product comprising at least olefin chlorohydrin; (c) contacting at least the olefin chlorohydrin with an aqueous alkali metal hydroxide to form an aqueous salt solution product containing at least epoxide; and (d) isolating the epoxide from the aqueous salt solution; wherein water is recovered from the product of at least Step (b) and recycled into Step (a) for use in forming the low chlorides aqueous hypochlorous acid (HOCl) solution. In this process, not only is the water internally recycled after Step (b), but a concentrated brine solution is generated in both Steps (a) and (d) which is useful in other processes such as electrochemical production of chlorine and caustic. The chlorine and caustic, in turn, may then be recycled back for use in forming the low chlorides aqueous HOCl solution. According to U.S. Pat. No. 5,486,627, it is generally preferred, prior to recycling into the chlor-alkali electrochemical cell, to remove any impurities from the brine. These impurities, it is disclosed typically comprise traces of organic solvent as well as HOCl decomposition products such as chloric acid and chlorate ion. A method for removing these impurities may include acidification and chlorine-based oxidation or absorption on carbon or zeolites.
Methods for removing impurities from brine before passing through a chlor/alkali electrochemical cell are disclosed in U.S. Pat. No. 5,532,389 to Trent et al, U.S. Pat. No. 4,126,526 to Kwon et al, U.S. Pat. No. 4,240,885 to Suciu et al, and U.S. Pat. No. 4,415,460 to Suciu et al. U.S. Pat. No. 5,532,389 to Trent et al discloses removing chlorates from a chloride brine by contacting the chlorates with acid to convert the chlorates to chlorine. Additionally, it is disclosed that by-product organic compounds, such as propylene glycol present in a brine stream containing alkylene oxide are advantageously removed through any oxidation, extraction or absorption process.
U.S. Pat. No. 4,126,526 to Kwon et al discloses an integrated process for electrolytic production of chlorine and the production of an olefin oxide via the chlorohydrin wherein the chlorohydrin is contacted with an aqueous solution of sodium hydroxide and sodium chloride from the cathode compartment of an electrolytic cell, to produce the oxide and brine. The brine is contacted with gaseous chlorine to oxidize organic impurities to volatile organic fragments, which are stripped from the brine, prior to recycling the brine to the electrolytic cell.
In the processes of the two Suciu et al patents, U.S. Pat. Nos. 4,240,885 and 4,415,460, organic impurities in aqueous salt solutions; e.g., alkali or alkaline earth chloride solutions in particular, brines, are oxidized with chlorate ions to convert organics to carbon dioxide. However the processes employ harsh reaction conditions of high temperatures, which are above 130 degrees centigrade (° C.), requiring high pressure equipment, a low pH of less than 5, most preferably less than 1, and chlorate ions which tend to form chlorinated organic compounds.
Conventional processes for purification of brine contaminated with organic impurities include biological treatment; oxidation with chlorine or hypochlorite; absorption over various absorption capable materials such as activated carbon; oxidation with hydrogen peroxide in the presence of dissolved or suspended catalysts or under UV irradiation conditions; oxidation with gaseous oxygen, air or oxygen enriched air in the presence of a dissolved or suspended catalyst; oxidation with ozone in combination with hydrogen peroxide or suspended catalysts. Electrical treatment of aqueous systems, including wastewater, is known, such as disclosed in U.S. Pat. No. 5,399,247 to Carey et al. and Martinez-Huitle et al., “Electrochemical Oxidation of Organic Pollutants for the Waster Treatment: Direct and Indirect Processes”, Chem. Soc. Rev., 2006, 35, 1324-1340, which are incorporated by reference herein in their entireties. However, such electrical treatment is not directed to the treatment of contaminated brine to reduce contaminants therein, or for use of the purified brine as process streams, including feed and recycle process streams.
Brine is generated by industrial processes that react chlorine atom-containing compounds with an inorganic base such as sodium hydroxide to form an aqueous brine solution containing chloride salts. Examples include the production of epichlorohydrin by reacting chlorohydrins with sodium hydroxide, the production of epoxy resins by reacting epichlorohydrin with polyphenolic compounds, such as bisphenol A or bisphenol F, in which the base reacts with chlorine atoms of the epichlorohydrin and the phenolic hydrogen atoms, and scrubbing of industrial effluent to remove hydrogen chloride from a chemical stream by reacting the hydrogen chloride with sodium hydroxide, such as in the hydrogen chloride absorber used to remove hydrogen chloride during the phosgenation process used to make isocyanates. The aqueous brine solutions produced by such processes often contain one or more organic compounds (associated with the processes) from which the brine is derived.
Aqueous brine solutions containing sodium chloride as the predominant salt are useful for the production of chlorine gas and sodium hydroxide or hypochlorite by an electrolytic process known as the chlor-alkali process. Chlorine gas, hypochlorite and sodium hydroxide produced by a chlor-alkali process are useful in a number of industrial processes in which chlorine atoms and/or a strong base is/are required. It would be desirable to be able to use aqueous brine solutions produced by industrial processes in the chlor-alkali process to integrate industrial chemical processes and thereby reduce raw material acquisition and byproduct disposal costs.
A problem associated with using aqueous brine solutions produced by industrial processes in the chlor-alkali process is that the presence of impurities such as organic compounds in such aqueous brine solutions must generally be reduced to a very low concentration, because the chlor-alkali process has a low tolerance for impurities, including organic compounds, and/or because products of high purity made from such chlor-alkali process, such as high purity sodium hydroxide, are desired. Generally, the organic compound concentration in aqueous brine used in industrial chlor-alkali production should be less than 50 ppm, and preferably should be less than 10 ppm, total organic carbon (TOC).
A known method for reducing the organic compound concentration in aqueous brine solutions is to conduct chlorinolysis to oxidize organic compounds to more volatile oxidation fragments and/or carbon dioxide that can be stripped from the aqueous brine solution. Chlorinolysis is generally carried out by introducing chlorine gas or hypochlorite into the aqueous brine solution at an elevated temperature. Such a process is disclosed, for example, in U.S. Pat. No. 4,240,885.
A disadvantage of relying solely on chlorinolysis for removal of organic compounds is that substantial amounts of chlorine gas or hypochlorite is generally required to reduce the organic compound concentration to an acceptable level when the initial organic compound concentration prior to chlorinolysis is relatively high. In that case, the purification process consumes a substantial portion of the chlorine gas or hypochlorite generated by the chlor-alkali process to thereby reduce the availability of the chlorine gas or hypochlorite generated by the chlor-alkali process for other industrial processes.
Another disadvantage of relying solely on chlorinolysis is that certain types of compounds such as acids and acid esters are generally more difficult to oxidize to break them down into oxidation fragments sufficiently volatile to be stripped from the aqueous brine solution. Reducing the concentration of such oxygen-containing compounds to an acceptable level via chlorinolysis is difficult and expensive.
Another disadvantage of relying solely on chlorinolysis is that it requires treatment of the vapor stream stripped from the brine solution to prevent discharge of chorine gas, hypochlorite and any chlorinated hydrocarbons into the environment.
Opportunities therefore remain to further improve the purification of aqueous brine solutions containing organic compounds so that the brine can be used for chlor-alkali electrolysis.